Pressurization system for high pressure processing system

ABSTRACT

The invention relates to a pressurization unit for use in processing equipment handling high pressure fluid, where the pressurization unit comprises at least one inlet and an outlet, the pressurization unit being adapted to receive a feed fluid at a feed pressure level at the inlet, being adapted to isolate the received feed fluid from the inlet and from the outlet and being adapted to increase the pressure of the fluid to a higher predetermined level and further being adapted to output the fluid through the outlet into the high pressure process while still isolated towards the inlet.

FIELD OF THE INVENTION

The present invention relates to the area of pressurization systems, inparticular pressurization systems for use in high-pressure continuousprocessing systems, where a need for increase the pressure of a lowpressure input feed stream to a high process pressure is present.

BACKGROUND OF THE INVENTION

Numerous applications of high-pressure continuous processes exist or areunder development or in early stages of commercialization. Examples ofsuch processes are hydrothermal and solvothermal processes e.g. forproduction of hydrocarbons such as transportation fuels, lubricants,speciality chemicals, gases, carbonized products and nanomaterials.

When processing e.g. bio-materials, these will have an abrasive effecton the pressurization equipment, in particular when operating at highpressure and high temperature. Further the bio-material may contain asignificant amount of fibres, in particular soft fibres that may preventnormally used check valves in closing. Due to the lack of completeclosure the fluid may stream at very high speed that will cut or have anabrasive effect on the check valves, in particular the valve seats.Further a loss of pressure will be the result of an insufficientsealing, which again may have a damaging effect on pumps or otherequipment.

Common for high pressure process equipment using these known methods andequipment is that the wear may still be significant due to the contentof abrasive material in the flowing liquid or the possibility ofinsufficient closing and since the flow velocity over the pressurizationarrangements is significant. As a result the known pressurizationsystems may be unreliable and hence making the entire high pressureprocessing system unreliable.

OBJECTIVE OF THE INVENTION

The object of the present invention is to therefore provide for apressurization unit, a pressurization arrangement as well as a method ofoperating such system that increases the reliability of thepressurization system and hence the reliability of the process systeminto which it is implemented.

DESCRIPTION OF THE INVENTION

In one aspect of the invention the objective is achieved through apressurization unit for use in processing equipment handling highpressure fluid, where the pressurization unit comprises at least oneinlet and an outlet, the pressurization unit being adapted to receive afeed fluid at a feed pressure level at the inlet, being adapted toisolate the received feed fluid from the inlet and from the outlet andbeing adapted to increase the pressure of the fluid to a higherpredetermined level and further being adapted to output the fluidthrough the outlet into the high pressure process while still isolatedtowards the inlet.

Advantageously the unit comprises an actuated valve at the inlet and anactuated valve at the outlet and further a pressurization device betweenthe inlet valve and the outlet valve.

In an embodiment means are provided for measuring the pressure upstreamthe inlet valve, between the inlet valve and the outlet valve anddownstream the outlet valve.

In a further embodiment a position indictor is provided indicating thecycle position of the pressurization device and being adapted to providea control signal for opening and closing of at least one valve in thepressurization unit.

In a further embodiment a position indicator is provided indicating thecycle position of the pressurization device and being adapted togenerate a measure for the flow volume, e.g. by calculating the volumeof the piston movement multiplied with the number of cycles per timeunit.

Preferably the unit comprises a pressurization device having a cylinderand a piston as well as means for driving the piston inside thecylinder.

In an embodiment the unit further comprises a control system, where thecontrol system is adapted to allow opening of the valves when a certainmaximum pressure difference is present between either sides of the valveto be opened.

Advantageously the inlet valve after having allowed inlet of a feedstream is closed for a period before the outlet valve is opened, herebyallowing pressure to be generated by the pressurization device.

Advantageously the outlet valve is closed for a period before the inletvalve is opened, hereby allowing pressure to be reduced in thepressurization device.

Hereby the overlap of closed inlet and outlet valves may correspond tobetween 5 and 30% of the working cycle, preferably between 10 and 20% ofthe working cycle.

In a further aspect of the invention the objective is achieved through apressurization arrangement comprising two or more pressurization unitsaccording to any of the preceding claims, the pressurization units beingarranged in parallel and/or in series.

Hereby the working cycles of the pressurization devices are preferablyevenly distributed corresponding to the number of pressurization units.

In an embodiment a position indicator is provided for a pressurizationdevice, indicating the cycle position of the device and being adapted toprovide a control signal for controlling the distribution of thepressurization device cycles.

In a still further aspect of the invention the objective is achievedthrough a method for pressurizing a high pressure processing system, themethod comprising entering a volume of pressurized fluid into apressurization device, closing the entry of pressurized fluid andpressurizing the entered volume to a desired pressure level bydecreasing the pressurization device volume, removing the fluid at thedesired pressure level from the pump by further reducing the pumpvolume.

Hereby the speed of the pressurization device is advantageously in therange 5-50 cycles per minute, preferably 5-25, most preferred 5-15cycles per minute.

In an advantageous embodiment a control signal generated as an outputfrom a pressure reduction system measurement, is used to control thepressurization unit or pressurization arrangement.

The invention further relates to a high pressure process systemcomprising a pressurization unit or a pressurization arrangementaccording to any of the preceding claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will in the following be described with reference to oneembodiment illustrated in the drawings where:

FIG. 1 shows a schematic overview of an embodiment of a pressurizationsystem;

FIG. 2 shows a schematic overview of a pressure reduction system to beused in a system incorporating a pressurization system;

FIG. 3 shows a schematic overview of a further embodiment of a pressurereduction system; and

FIG. 4 shows a schematic overview of a double action pressurereduction/pressurizing system.

FIG. 5 shows schematically a coupling of an energy reservoir to agenerator;

FIG. 6 shows schematically a single pressure reduction device/pressuringdevice;

FIG. 7 shows schematically a double action pressurization system and adouble action pressure reduction system;

FIG. 8 shows schematically the opening and closing of inlet and outletvalves during a cycle of a pressurization pump;

FIG. 9 shows schematically the opening and closing of inlet and outletvalves during a cycle of a pressure reduction pump;

FIG. 10 shows a schematic overview of a pump piston with cooling;

FIG. 11 shows a schematic overview of an embodiment for continuous highpressure process for conversion of carbonaceous materials such asbiomass to renewable oil; and

FIG. 12 shows an advantageous embodiment of a continuous high pressureprocess for hydrothermal transformation of carbonaceous materials suchas biomass in to renewable fuels;

DESCRIPTION OF AN EMBODIMENT

From FIG. 1 a pressurization pump arrangement is shown. The pumparrangement comprises three pumps 3′adapted to receive a feed stream 1′of material to be processed at a relatively low pressure andsuccessively pressurizing the feed stream to a significantly higherprocess pressure feed stream 2′. The inlet and outlet to and from thepressurization pump 3′are controlled by actuated valves 4′,5′. Pressureis supplied through supply lines 7′,8′ through control valves 9′.

The pressurization pumps 3′ may be driven entirely by a force generatedby hydraulic pumps or by electrical motors. Alternatively or as asupplement, energy absorbed from the pressure reduction processdescribed above in connection with FIG. 1 may be used to provide for atleast part 7′ of the pressurization of the feed stream. Further aposition indicator 35 is shown, which will be able to indicate theposition of the piston, and which again may be used to calculate thecylinder volume at a given position. Pressure transducers are providedupstream, between and downstream the valves 4′,5′ and are connected to acontroller that will be able to provide control signals to the valves4′,5′ regarding opening and closing of these based on the input from thepressure transducers and a predetermined control strategy.

From FIG. 2 a pressure reduction arrangement is shown. The pressurereduction arrangement comprises three pumps 3, each with a high pressureinlet 1 and a lower pressure outlet 2 for a process stream. The inletand the outlet are controlled by valves 4,5. The pump 3 as such is apiston pump with a certain stroke. The piston in the main cylinder isconnected to an actuator cylinder capable of exercising a pressure onthe piston or conveying the pressure from the high pressure processstream into storage 6. Pressure supply to operate the pump for part ofits operation is supplied through 8 and controlled by valve 9. Therecovered energy may be conveyed through conduit 7. Further a positionindicator 35 is shown, which will be able to indicate the position ofthe piston, and which again may be used to calculate the cylinder volumeat a given position. Pressure transducers are provided upstream, betweenand downstream the valves 4,5 and are connected to a controller thatwill be able to provide control signals to the valves 4,5 regardingopening and closing of these based on the input from the pressuretransducers and a predetermined control strategy.

From FIG. 3 a single unit de-pressurization pump appears. The unitcomprises a pump cylinder 3, a servo cylinder 11 and a control cylinder13. The servo cylinder at the piston 12 in this is driven by pressurefrom energy recovery and the control cylinder 13 with its piston 14 isdriven by pressure from a high pressure hydraulic pump. Pressure issupplied and recovered through supply lines 15,16,17,18 controlled byvalves 19,20

From FIG. 4 a combined unit is shown where the high pressure inlet pumpand the pressure reduction pump are connected. Only a single unit 3,3′is shown however typically two or more units are present. The reason forproviding are for example that a certain redundancy is needed forallowing repair or maintenance on a single unit without interrupting theprocess operation and further the presence of two or more pump unitswill reduce pressure fluctuations and hence provide for less pressurecaused stress in the system. The slower the system is operating, i.e.the lower the number of strokes per minute of the pumps, the less thesize of the pressure fluctuations will be. Any need for supplyingadditional pressure will take place through control valve 22 to theservo cylinder 21.

FIG. 5 schematically shows the coupling of an energy reservoir 6 to agenerator 23. A low pressure turbine will typically be the driving meansfor the generator, however for the sake of simplicity this has not beendepicted.

FIG. 6 schematically shows a cylinder-piston 3,3′,26 arrangement capableof acting as a pressure reduction device or as a pressurization device.The inlet and outlet valves 4,4′,5,5′ appear in connection with thepressure reduction/pressurization cylinder 3,3′ and further the controlcylinder 25 for providing a hydraulic control of the movement of thepiston 26 is shown. The control cylinder comprises a piston 27 andcontrol pressure fluid inlets/outlets 29,30. An additional inlet/outletis shown in connection with main cylinder 3,3′.

From FIG. 7 a system appears where in connection with the HTL process apressurization unit 3′,11′,13′,19′,20′,2′ as well as a pressurereduction device 3,4,11,13,19,20 has been introduced. The pressurizationand the pressure reduction devices are double acting devices where inconnection with the pressure reduction device the additionalcylinder-piston arrangement serves the purpose of recovering energy fromthe pressure reduction process and where the additional cylinder pistonarrangement in connection with the pressurization device serves thepurpose of utilizing the recovered energy from the pressure reductionprocess. Additional pressure may be applied to the pressurization devicedue to loss in the system.

FIG. 8 shows the opening and closing of inlet and outlet valves of apressurization device, in a view where the stroke of a piston in acylinder is depicted as well. Three cycles are depicted for two parallelpressurization units. It appears that the cylinder is filled with slurryas the piston moves downwards and the valve V5 is open. Valve V5 closesshortly before the piston reaches the bottom position. As the pistonmoves upwards the slurry is pressurized and when valve V6 is opened andthe fluid in the cylinder volume is forced out of the cylinder throughthe outlet and into the HTL process. Shortly before reaching the topposition for the piston the valve V6 closes and the remaining fluid inthe cylinder is de-pressurized to the pressure existing on the processside of valve V5. When the piston has moved slightly from its topposition the pressure difference between the cylinder and upstream areaare essentially identical and the valve V5 can open for an additionalcycle.

Same procedure is shown for an additional pressure reduction deviceoperating simultaneous with the one described above. Valves V7 and V8carries out the same tasks as described above, however the entire cycleis displaced corresponding to a half cycle in order to minimise pressurefluctuations in the system.

FIG. 9 shows the opening and closing of inlet and outlet valves of apressure reduction device, in a view where the stroke of a piston in acylinder is depicted as well. Three cycles are depicted for two parallelpressure reduction units. It appears that the cylinder is filled as thepiston moves downwards and the valve V1 is open. Valve V1 closes shortlybefore the piston reaches the bottom position. As the piston movesfurther towards the bottom position the pressure is reduced. As thepiston moves upwards the valve V2 is opened and the fluid in thecylinder volume is forced out of the cylinder through let outlet.Shortly before reaching the top position for the piston the valve V2closes and the remaining fluid in the cylinder is pressurized to thepressure existing on the process side of valve V1. When the pistonreaches its top position the pressure difference between the cylinderand the process area are essentially identical and the valve V1 can openfor an additional cycle.

Same procedure is shown for an additional pressure reduction deviceoperating simultaneous with the one described above. Valves V3 and V4carries out the same tasks as described above, however the entire cycleis displaced corresponding to a half cycle in order to minimise pressurefluctuations in the system.

FIG. 10 shows a pump cylinder 3 and piston 26 arrangement where thepiston comprises cooling channels ensuring that the temperature can bekept at a suitable level. The cooling channels 32,33 extent through thepiston rod 31 to the piston 26, where a cooling media can be circulatedin channels 34.

FIG. 11 and FIG. 12 shows HTL processes that are further explained inthe following.

Pressurization or Pressure Reduction Unit

The pressure reduction unit can consist of two or more piston pumps,that can be controlled in a way that use any number of pumps howeverpreferably at least two pumps. A piston pump comprises a cylinder with apiston and valves for inlet and outlet as well as driving means forapplying a force or receiving a force to/from the piston.

The pumps are designed as a hydraulic pressure de-amplifier with a ratiothat meets operating conditions. The de-amplification is achievedthrough the dimensioning of the pressurized surface area of the pistons.In negative amplification (an attenuation or damping) may be achievedthrough an opposite variation of the pressurized surface areas.

Pumps are designed in a way that allows cleaning of the pump interior.Reducing dead space at maximum stroke ensures this.

By minimizing obstructions such as valves and guide channels non-activevolume on top of piston at maximum piston stroke is eliminated. Too muchdead space at full stroke leaves more residual feed material incylinder.

When not having dead volume at maximum piston stroke there is limitedspace for residual biomass, which makes cleaning much easier sincealmost no feed material is left behind after each stroke.

Another advantage by reducing dead space is to prevent build-up ofunprocessed feed material inside the pump unit.

Pump Control

In order to determine the piston position in a cylinder, positioners arebuilt in to the piston rod, so that the piston position is known at anygiven moment. This helps controlling pressure and flow in cylinder.

Pressure is measured by built in pressure transmitters. Pressuretransmitters are built in to top of each cylinder so pump conditions arealways monitored. If pressure transmitters are not built in to thecylinder top and built into the following tubing after control valves itis impossible to ensure 0 bar Δp over control valves.

Minimum Δp over control valves ensure minimum wear from possibleabrasives in feed as well as minimum mechanical wear else caused by highphysical pressure towards valve seats.

Installing position sensors in cylinder piston rods makes it possible tomeasure flow through cylinder by aid of mathematical functions thattakes piston frequency, piston area and length of piston stroke in toaccount. Being able to manage piston position reduces pressurepulsations as control valves and piston position can be controlled veryaccurately making it possible to pressurize remaining content incylinder in order to eliminate Δp over control valves and therefore alsono pressure drop when opening control valves.

Δp Valves

Control cylinders by use of positioner so Δp across inlet/outlet valvesis reduced as much as possible in order to reduce wear of valve seats.Δp is reduced as much as possible by monitoring pressure on both sidesof the control valves by pressure transmitters while either compressingor decompressing media in cylinder to meet common pressure setting.

Position sensors are used in the control loop for timing the controlvalves, in a way that ensures enough feed material in cylinder tocompress to process pressure in filling mode and leave enough pistonstroke to ensure decompression before emptying the cylinder.

Pressure De-Amplifier

Hydraulic energy can be recovered at different pressures when usinghydraulic pressure de-amplifiers. The energy absorbed as a result of thepressure reduction may be stored as pressurised fluid or may be utiliseddirectly for driving e.g an electrical generator.

Flow Measurement

By use of incorporated positioners the piston position may be determinedand hence a measure for the processed flow through the pressurereduction unit.

Inlet/Outlet Valves

Valves used for controlling inlet and outlet of pressure reduction unitare typically of a controlled ball valve type. An actuator is used tocontrol the movement of the valves.

Filling/Emptying of Pressure Reduction or Pressurisation Unit

During filling the first pressure reduction or pressurization unit,counter pressure is held in the hydraulic cylinder during entire stroketo maintain a constant pressure in the pressure reduction orpressurization unit.

Before the first pressure reduction or pressurization unit has reachedthe end of its stroke a second pressure reduction unit has prepared bycompressing remaining fluid to operating pressure before opening inletvalve and taking over from first pressure reduction unit.

The first pressure reduction or pressurization unit can now decompresscontents by expanding cylinder to the end of stroke and empty cylindercontent by means of the hydraulic cylinder leaving enough in pressurereduction unit to compress media to operating pressure.

Maintenance

Main pressure reduction or pressurization arrangement comprising anumber of pressure reduction units, is constructed in a way that allowsreplacement of a pressure reduction unit segment during operation. Meansfor safe separation of a pressure reduction unit segment is a totalseparation from the operation of the unit in question throughappropriate valve arrangements. Further the remaining units may bereconfigured during a maintenance operation to be distributed over theworking cycle of the pressure reduction or pressurization arrangement inorder to avoid pressure fluctuations.

Seals

When necessary hydraulic seals are cooled in order to withstandoperating conditions.

Function of Pressure Let Down/Reverse Pump

Reverse pump cylinder 1 is filled through V1 until cylinder has reacheda given stroke that allows media to decompress by moving cylinder pistonfurther towards end of stroke. Before moving piston to end of stroke, V1closes.

After decompression V2 opens and the hydraulic cylinder presses thedecompressed fluid out of the cylinder to phase separation. Cylinder 1does not empty completely as it is necessary to withhold enough fluid topressurize to process pressure by compression with V2 closed.

The reason is to avoid pressure drop across V1 when it is time to reopenfor next filling.

Similarly when V1 closes, V3 opens. Before V3 can open the remainingfluid from the latter stroke is pressurized to prevent excessive wear ofvalve seats by avoiding high pressure drop.

FIG. 10 shows an embodiment of a continuous high pressure productionprocess for conversion of carbonaceous materials such as biomass torenewable oil comprising pumping means and pressurization means.

As shown on FIG. 10 , the carbonaceous material is first subjected to afeed mixture preparation step. The feed mixture preparation steptransforms the carbonaceous material into a pumpable feed mixture andgenerally includes means for size reduction of the carbonaceous andslurrying the carbonaceous material with other ingredients such aswater, catalysts and other additives such as organics in the feedmixture.

The second step is a pressurization step where the feed mixture ispressurized by pumping means to a pressure of at least 150 bar and up toabout 400 bar.

An advantageous pumping means are where the pressurization unitcomprises at least one inlet and an outlet, the pressurization unitbeing adapted to receive a feed fluid at a feed pressure level at theinlet, being adapted to isolate the received feed fluid from the inletand from the outlet and being adapted to increase the pressure of thefluid to a higher predetermined level and further being adapted tooutput the fluid through the outlet into the high pressure process whilestill isolated towards the inlet.

The pressurization unit preferably comprises an actuated valve at theinlet and a actuated valve at the outlet and further a pressurizationdevice between the inlet valve and the outlet valve. This is preferablyachieved by a pressurization device comprising a pump unit having acylinder and a piston as well as means for driving the piston inside thecylinder.

Preferably means are provided for measuring the pressure upstream theinlet valve, between the inlet valve and the outlet valve and downstreamthe outlet valve.

In one embodiment a position indicator is provided indicating the cycleposition of the pressure reduction device and being adapted to provide acontrol signal for opening or closing at least one valve in the pressurereduction system.

In a further embodiment a position indicator is provided indicating thecycle position of the pressurization device and being adapted togenerate a measure for the flow volume, e.g. by calculating the volumeof the piston movement multiplied with the number of cycles per timeunit.

In an embodiment the pressure reduction unit comprises a pressurereduction device comprising a cylinder and a piston as well as means fordriving the piston inside the cylinder.

In a further embodiment the pressure reduction unit may further comprisea control system, where the control system is adapted to allow openingof the valves when a certain maximum pressure difference is present oneither side of the valve to be opened.

The pressurized feed mixture is subsequently heated to a reactiontemperature in the range from about 300 and up to about 450° C.

The feed mixture is generally maintained at these conditions insufficient time for conversion of the carbonaceous material e.g. for aperiod of 2 to 30 minutes, such as in the range 3 to 20 minutes; andpreferably in the range 5 to 15 minutes, before it is cooled and thepressure is reduced.

The product mixture comprising liquid hydrocarbon product, water withwater soluble organics and dissolved salts, gas comprising carbondioxide, hydrogen, and methane as well as suspended particles from saidconverted carbonaceous material is subsequently cooled to a temperaturein the range 80° C. to 250° C. such as in the range 120 to 170° C.

The cooled product mixture thereafter enters a pressure reducing device,where the pressure reduction unit comprises at least one inlet and anoutlet, the pressure reduction unit being adapted to receive apressurized fluid at process pressure level at the inlet, being adaptedto isolate the received pressurized fluid from the upstream process andfrom the outlet and being adapted to reduce the pressure of the fluid toa lower predetermined level and further being adapted to output thefluid through the outlet while still isolated towards the upstreamprocess.

In general Pressure reduction unit comprises an actuated valve at theinlet and an actuated valve at the outlet and between the inlet valveand the outlet valve a pressurization device. Further a pressurereduction unit comprises means for measuring the pressure upstream theinlet valve, between the inlet valve and the outlet valve and downstreamthe outlet valve.

The pressure reduction unit may further comprise a pump unit having acylinder and a piston as well as means for driving the piston inside thecylinder. Advantageously the pressure reduction unit further comprises aposition indicator indicating the cycle position of the pressurereduction device and being adapted to provide a control signal foropening or closing at least one valve in the pressure reduction system.

In one embodiment the pressure reduction unit further comprises acontrol system, where the control system is adapted to allow opening ofthe valves when a certain maximum pressure difference is present oneither side of the valve to be opened.

Often the pressure reduction system is operated so that the inlet valveafter having allowed inflow of a feed stream is closed for a periodbefore the outlet valve is opened, hereby allowing the pressure to bereduced in pressure reduction device.

In order to minimize the pressure loss over the inlet valve and therebythe wear, the outlet valve may be closed for a period before the inletvalve is opened, hereby allowing pressure to be generated in thepressure reduction device in a predefined way. The overlap of closedinlet and outlet valves corresponds to between 5 and 30% of the workingcycle, preferably between 10 and 20% of the working cycle.

A pressure reduction arrangement typically comprises two or morepressure reduction units being arranged in parallel and/or in series.The working cycles of the individual pressure reduction units of thepressure reduction arrangement be evenly distributed corresponding tothe number of pressure reduction units.

Further the pressure reduction arrangement may include a positionindicator each pressure reduction device, indicating the cycle positionin the device and being adapted to provide a control signal forcontrolling the distribution of the pressure reduction unit cycles.

In general, the pressure in the high pressure processing system isreduced comprising entering a volume of pressurized fluid into apressure reduction device closing the entry of pressurized fluid andexpanding the entered volume to a desired pressure level by increasingthe pressure reduction device volume, removing the fluid at the desiredpressure level from the pressure reduction device by reducing thepressure reduction device volume.

The speed of the pump is in many applications in the in the range 5-50cycles per minute, preferably 5-25, most preferred 5-15 cycles perminute.

An advantageous embodiment of a pressure reduction device is where thepressure reduction pump is connected to a further pump that drives apressurization of the energy absorption reservoir. For example thepressure reduction device further comprising an energy reservoir, wherethe pump is operatively connected to the reservoir and where the energyabsorbed by the pump is converted and transferred to the reservoir forsuccessive utilization. In a preferred embodiment a pressurization pumpis provided for supplying additional pressure to the input side of thepressurization equipment in order to compensate for loss of pressureenergy in the system.

In a preferred embodiment, the energy reservoir drives a pressurizationpump adapted to pressurize the feed mixture in the pressurization step(step 2 above) of the high pressure process. In one embodiment, this isperformed by a low pressure turbine connected to a generator generatingelectrical energy, and the electricity generated reduces the energyrequired to drive the pressurization pump in the pressurization step.

The converted feed mixture is further separated into at least a gasphase, a renewable crude oil phase, a water phase with water solubleorganic compounds as well as dissolved salts and eventually suspendedparticles. The separation may be performed by gravimetric phaseseparation or other suitable means such as centrifugation.

The renewable crude oil may further be subjected to upgrading theprocess where it is pressurized to a pressure in the range from about 20bar to about 200 bars such as a pressure in the range 50 to 120 bar,before being heated to a temperature in the range 300 to 400° C. in oneor more steps and contacted with hydrogen and heterogeneous catalyst(s)contained in one or more reaction zones, and eventually fractionatedinto different boiling point fractions.

FIG. 11 shows an advantageous embodiment of a high pressure process forhydrothermal transformation of carbonaceous such as biomass in torenewable transportation fuels, lubricants and/or fine chemicalscomprising pressurization and a pressure let down system.

1. Preparation of Feed Mixture

The first step of the process is to prepare a feed mixture in the formof a pumpable slurry of the carbonaceous material. This generallyincludes means for size reduction and slurrying such as dispersing theorganic matter with other ingredients such as water, catalysts and otheradditives such as organics in the feed mixture,

A carbonaceous material may be in a solid form or may have a solidappearance, but may also be in the form of a sludge or a liquid. Furtherthe carbonaceus material(-s) may be contained in one or more inputstreams.

Non limiting examples of carbonaceous feedstock include biomass such aswoody biomass and residues such as wood chips, saw dust, forestrythinnings, road cuttings, bark, branches, garden and park wastes &weeds, energy crops like coppice, willow, miscanthus, and giant reed;agricultural and byproducts such as grasses, straw, stems, stover, husk,cobs and shells from e.g. wheat, rye, corn rice, sunflowers; empty fruitbunches from palm oil production, palm oil manufacturers effluent(POME), residues from sugar production such as bagasse, vinasses,molasses, greenhouse wastes; energy crops like miscanthus, switch grass,sorghum, jatropha; aquatic biomass such as macroalgae, microalgae, cyanobacteria; animal beddings and manures such as the fibre fraction fromlive stock production; municipal and industrial waste streams such asblack liquor, paper sludges, off spec fibres from paper production;residues and byproducts from food production such as juice or wineproduction; vegetable oil production, sorted municipal solid waste,source sorted house wastes, restaurant wastes, slaughter house waste,sewage sludge and combinations thereof.

Many carbonaceous materials are related to lignocellulose materials suchas woody biomass and agricultural residues. Such carbonaceous materialsgenerally comprise lignin, cellulose and hemicellulose.

An embodiment includes a carbonaceous material having a lignin contentin the range 1.0 to 60 wt % such as lignin content in the range 10 to55% wt %. Preferably the lignin content of the carbonaceous material isin the range 15 to 40 wt % such as 20-40 wt %.

The cellulose content of the carbonaceous material is preferably in therange 10 to 60 wt % such as cellulose content in the range 15 to 45% wt%. Preferably the cellulose content of the carbonaceous material is inthe range 20 to 40 wt % such as 30-40 wt %.

The hemicellulose content of the carbonaceous material is preferably inthe range 10 to 60 wt % such as cellulose content in the range 15 to 45%wt %. Preferably the cellulose content of the carbonaceous material isin the range 20 to 40 wt % such as 30-40 wt %.

Depending on the specific organic matter being transformed and how it isreceived, the size reduction may be conducted in one or more steps e.g.the carbonaceous material may be treated as is and subsequently mixedwith other ingredients in the same step or it may pre-grinded to a sizesuitable for further processing and size reduction in the mixing step.Often the carbonaceous material is size reduced to a particle size lessthan 10 mm such as a particle size of less than 5 mm the pre-grindingstep; preferably to a particle size of less than 3 mm such as less than2 mm.

The pre-grinding may according to an embodiment be performed using ashredder, cutting mill, hammer mill, pan grinder, impeller mill or acombination thereof.

Advantageously the pre-grinding step may further comprise means forremoval of impurities such as metals, stones, dirt like sand, and/or toseparate off spec fibres from the carbonaceous material with particlesize with said maximum size. Such means may comprise magneticseparation, washing, density separation such as flotation, vibrationtables, acoustic separators, sieving and combinations thereof. Saidmeans may be present prior to the pre-grinding step and/or after thepre-grinding step.

The carbonaceous material is subsequently mixed with other ingredientsof the feed mixture. Other ingredients may include:

1. Recycled oil (hydrocarbons) produced by the process or a fraction ofthe oil (hydrocarbon produced by the process; preferably in a weightratio to dry ash free organic matter in the range 0.5 to 1.5 such as aratio 0.8 to 1.2;

2. Recycled concentrate of the water phase from the process comprisingrecovered homogeneous catalyst and water soluble organics such as one ormore components selected from

a. Ketones such as acetone, propanones, butanones, penthanones,penthenones, cyclopentanones such as 2,5 dimethyl cyclopentanone,cyclopentenones, hexanones and cyclohexanones such as 3-methyl hexanone,quionones etc.

b. Alcohols and poly alcohols such as methanol. ethanol, propane's (inclisopropanol), buthanols, penthanols, hexanols, heptanols, octanols suchas 2-butyl-1-octanol, hydroquinones etc

c. Phenols, alkylated phenols, poly-phenols, monomeric and oligomericphenols, creosol, thymol, alkoxy phenols, p-coumaryl alcohol, coniferylalcohol, sinapyl alcohol, flavenols, catechols

d. Carboxylic acids such as formic acid, acetic acid and phenolic acidslike ferric acid, benzoic acids, coumarin acid, cinnamic acid, abieticacid, oleic acid, linoleic acid, palmetic acid, steric acid

e. Furans such as THF etc

f. Alkanes, alkenes, toluene, cumene etc. and combinations thereof.

In general the water soluble organics constitute a complex mixture ofthe above and the feed mixture may comprise such water soluble organicsin a concentration from about 1% by weight to about 10% by weight suchas in the range from about 2% by weight to about 5% by weight.

3. Make up homogeneous catalyst in form a potassium carbonate and/orpotassium hydroxide and/or potassium acetate; preferably added in theform of an aqueous solution and added in an amount so that the totalconcentration of potassium in the resulting feed mixture is at least0.5% by weight such as a concentration in the feed mixture of at least1.0% by weight; preferably the concentration of potassium is at least1.5% by weight such as at least 2.0% by weight;

4. Make up base for pH adjustment. Preferably sodium hydroxide is addedto the feed mixture in an amount so as the pH measured in the recycledwater phase is above 7 and preferably in the range 8.0 to 12.0 such asin the range 8.0 to 10.0.

The ingredients 1.-4. are preferably all on a liquid form and mayadvantageously be premixed and optionally preheated, before being mixedwith the organic matter to produce said feed mixture. Premixing and/orpreheating may reduce loading time and heating time required in themixer.

The mixing of the carbonaceous material and other ingredients are mixedso as to form a homogeneous slurry or paste. Said mixer may be a stirredvessel equipped with means for efficiently mixing, dispersing andhomogenizing viscous materials such as a planetary mixer, Kneader orBanbury mixer. The mixer is preferably further equipped with means forheating said feed mixture to a temperature in the range 80 to 220° C.,preferably in the range 130 to 200° C. and more preferably in the range150 to 180° C. at sufficient pressure to avoid boiling such as apressure in the range 1-30 bars, preferably in the range 4-20 bars suchas in the range 5-10 bars. Heating the feed mixture to temperatures inthe above ranges results in a softening and/or at least partlydissolution of the carbonaceous thereby making the feed mixture easierto size reduce and homogenize. Preferred means for heating said feedmixture during the preparation include a heating jacket. In a preferredembodiment the heat for preheating said feed mixture is obtained fromthe cooling of the converted carbonaceous material comprising liquidhydrocarbon product e.g. by heat exchange with this process stream.Hereby the energy efficiency of the process may be further enhanced. Themixer may further be equipped with a re-circulation loop, where materialis withdrawn from said mixer and at least partly re-circulated in aninternal or external loop and re-introduced into said mixer so as tocontrol the feed mixture characteristics e.g. rheological propertiessuch as viscosity and/or particle size to a predefined level. Theexternal loop may further comprise one or more size reduction and/orhomogenization device(-s) such as a macerator and/or a colloidal milland/or a cone mill or a combination thereof in a series and/or parallelarrangement. The feed mixture produced may be fed to a holding tankbefore entering the pressurization step of the process.

Preferably, the carbonaceous material is fed to the mixer graduallyrather than at once to control the viscosity of the feed mixture andthat feed mixture remains pumpable, while being size reduced andhomogenized. The control of the viscosity may be performed by measuringthe power consumption of the mixer and/or colloidal mill and addingorganic matter to the feed mixture according to a predefined powerconsumption. It is further advantageous not to empty the mixercompletely between batches as the prepared feed mixture acts as atexturing agent for the next batch and thereby assists in homogenizingthe next batch by making it more pumpable, and thereby the carbonaceousmaterial may be added faster.

Other preferred means for thoroughly mixing and homogenizing theingredients in the feed mixture include inline mixers. Such inlinemixers may further introduce a cutting and/or a scissoring and/or aself-cleaning action. An preferred embodiment on such inline deviceinclude one or more extruders.

Typically the dry content of carbonaceous material in the feed mixtureis in the range 10 to 40% by weight, preferably in the range 15 to 35%and more preferably in the range 20 to 35% by weight.

The process requires water to be present in said feed mixture. Typicallythe water content in said feed mixture is at least 30% by weight and inthe range 30 to 80% by weight and preferably in the range 40 to 60%.

2. Pressurization

The second step of an advantageous embodiment of a high pressure processis pressurization to the desired pressure for said conversion process.Said pressurization to the desired reaction pressure is essentiallyperformed before heating from entry temperature from the feed mixture tothe reaction temperature is initiated.

Typically the feed mixture is pressurized to an operating pressureduring said heating and conversion of at least 150 bars such as 180bars, preferably said operating pressure is at least 221 bars such as atleast 250 bars and more preferably said operating pressure duringconversion is at least 300 bars.

Even more preferably the operating pressure is in the range of 300-400bars such as in the range 300-350 bars.

Many embodiments relates to processing of feed mixtures with a highcontent of carbonaceous material as described above. Such feed mixturestypically have densities in the range 1050 to 1200 kg/m3, and typicallybehaves as a homogeneous pseudoplastic paste rather than a suspension ofdiscrete particles (liquid). The viscosity of such pastes may varywidely with shear rate due to the pseudoplastic (shear thinning)behavior and may be in the 10³ to 10⁷ cP depending of the specific shearrate and carbonaceous material being treated.

An aspect relates to a pressurization system for pressurizing suchhighly viscous pseudoplastic feed mixtures. The pressurization systemcomprises two or more pressure amplifiers each comprising cylinders witha piston equipped with driving means for applying and/or receiving aforce to the piston such as shown and described in connection with FIG.2-9 . Advantageous driving means for the pistons in the cylindersinclude hydraulically driven means.

The surface area of the pistons is typically dimensioned so as toamplify the pressure i.e. the surface area of each end of the piston isdimensioned so as to obtain a predefined pressure ratio on each side ofthe piston. The ratio of surface area on the low pressure side of thepiston to the surface area on the high pressure side of the piston maybe in the range 1 to 20 such as in the range 1 to 10. Preferably theratio of surface area on the low pressure side of the piston to thesurface area on the high pressure side of the piston is in the range 1to 3 such as in the range 1 to 2.

The pressure amplifiers are typically designed for low stroke speeds(large stroke volume) thereby allowing for the use of actuated valvesfor filling and emptying of the cylinders rather than check valves.Preferred actuated valves according to the present invention includegate valves and ball valves or a combination thereof.

The stroke speed of the pistons may be from about 1 stroke per minute upto about 150 strokes per minute such as from about 5 strokes per minuteup to about 100 strokes per minute. Preferably the stroke speed of thepistons are from about 10 to about 80 strokes per minute such as astroke speed of the piston in the range 20 strokes per minute to about60 strokes per minute. Besides allowing for the use of actuated valvesthe low stroke speed of the piston reduces the wear on pistons, sealsand valve seats.

Often the pressure amplifiers are further designed as double actingpistons as shown in FIG. 1 .

The pressure amplifiers according to an embodiment are further designedso as to maximize the cleaning effect of the piston by minimization ofthe dead space in the cylinder. Pumps are designed in a way that allowscleaning of the pump interior. Reducing dead space at maximum strokeensures this. The may be performed by minimizing obstructions such asvalves and guide channels and thereby non-active volume on top of pistonat maximum piston stroke is eliminated. Too much dead space at fullstroke leaves more residual feed material in cylinder. When not havingdead volume at maximum piston stroke there is limited space for residualbiomass, which makes cleaning much easier since almost no feed materialis left behind after each stroke. Another advantage by reducing deadspace is to prevent build-up of unprocessed feed material inside thepump unit.

Still further the pressure amplifiers may be equipped with positionersto monitor and control the position of the piston at any given moment.The piston positioners are preferably incorporated into the cylinderrod. The positioners are used to control the position of the piston. Thepositioners of the pressure cylinders may also be used to extract a flowmeasurement of media being pressurized by the both individual cylinderand the pressurization system i.e. the volumetric flow rate of theindividual cylinder is given by the stroke volume multiplied by thenumber of strokes over a given time interval, and the same totalvolumetric flow rate may be extracted as the sum of the volumetric flowmeasurements of the individual cylinders.

The positioner(-s) may further be used for synchronization of thestrokes of the individual pressure amplifiers e.g. when the feed in acylinder is being pressurized, another cylinder(s) is being charged withfeed mixture. After the cylinder has been charged, the cylinder ispre-pressurized to a pre-defined level by initiating the stroke with thevalve towards the process closed. When the first cylinder has reached acertain stroke length, the actuated valve towards the process is closedand the equivalent valve towards the process for the next cylinder withpre-charged and pre-pressurized feed mixture to be pressurized isopened. By applying such sequence according to an embodiment thepressure drop over the actuated valve towards the process andconsequentially valve wear and pressure fluctuations are minimized.

In order to determine the piston position in a cylinder, positioners arebuilt in to the piston rod, so that the piston position is known at anygiven moment. This helps controlling pressure and flow in cylinder.

Pressure is measured by built in pressure transmitters. Pressuretransmitters are built in to top of each cylinder so pump conditions arealways monitored.

If pressure transmitters are not built in to the cylinder top it andonly built into the following tubing before and after control valves itis impossible to ensure 0 bar Δp over control valves.

Minimum Δp over control valves ensure minimum wear from possibleabrasives in feed as well as minimum mechanical wear else caused by highphysical pressure towards valve seats.

Installing position sensors in cylinder piston rods makes it possible tomeasure flow through cylinder by aid of mathematical functions thattakes piston frequency, piston area and length of piston stroke in toaccount. Being able to manage piston position reduces pressurepulsations as control valves and piston position can be controlled veryaccurately making it possible to pressurize remaining content incylinder in order to eliminate Δp over control valves and therefore alsono pressure drop when opening control valves.

Control cylinders by use of positioner so Ep across inlet/outlet valvesis reduced as much as possible in order to reduce wear of valve seats.Δp is reduced as much as possible by monitoring pressure on both sidesof the control valves by pressure transmitters while either compressingor decompressing media in cylinder to meet common pressure setting.

Position sensors are used in the control loop for timing the controlvalves, in a way that ensures enough feed material in cylinder tocompress to process pressure in filling mode and leave enough pistonstroke to ensure decompression before emptying the cylinder.

The pressure fluctuations may be further reduced by the use of at least2 and preferably 3 or more pressure amplifiers in a parallel arrangementaccording to an embodiment. The control of the individual pressureamplifiers may be adapted so they are operated in a sequential manner todamp and minimize pressure fluctuation when switching from one pressureamplifier to the next.

For many embodiments, where 3 or more cylinders are present these areequipped with sealing means such as double valves so that an individualcylinder can be sealed off and safely exchange an individual cylinder,while other cylinders are kept operating. A more robust, easy tomaintain pressurization arrangement having a high availability is herebyobtained.

A pressurization arrangement according to an advantageous embodimentincludes withdrawing the feed mixture from the feed mixture preparationstep 1. described above, often via a holding tank, and transferring thefeed mixture to the pressurization step by a pre-charging pump. Thepre-pressurization pump or the pre-charging of the pressurization stepis preferably a positive displacement pump such as a piston pumpprogressive cavity pump, lobe pump, rotary gear pump, auger pump, orscrew pump. Due to the shear thinning characteristics of the feedmixtures according to many embodiments, the holding tank may be equippedwith agitation means in order to induce shear on the feed mixture andthereby reduce the viscosity before being charged to pressure amplifyingcylinders. The shear and agitation of the holding tank may also be atleast partly introduced by re-circulation of part of the feed mixturebeing withdrawn from the holding tank by the pre-charging pump.

The inlet temperature to the pressure amplifying cylinders is generallyin the range from about 10° C. to about 250° C. such as from about 20°C. to about 220° C.; preferably the inlet temperature to the pressureamplifying cylinders is in the range from about 50° C. to about 210° C.such as from about 80° C. to about 200° C.; even more preferably theinlet temperature to the pressure amplifying cylinders is in the rangefrom about 100° C. to about 180° C. such as from about 120° C. to about170° C.

For applications, where the temperature exceeds about 120° C. such asabout 140° C., the cylinders may further be equipped with means forcooling the seals of piston in order to withstand the operatingconditions as shown and described in connection with FIG. 9 above.

In an advantageous embodiment pressure energy is recovered in thepressure reduction step described below under step 6. Pressurereduction, and transferred to an energy absorption reservoir, where theenergy absorbed by the pressure reducing device is transferred to thereservoir for successive utilization in e.g. the pressurization step.Thereby a very energy efficient high pressure process is obtained.

3. Heating

The pressurized feed mixture is subsequently heated to a reactiontemperature in the range 300 to 450° C. such as in the range 350 to 430°C., preferably in the range 370 to 430° C. such as in the range 390 to430° C., more preferred in the range 400 to 420° C. such as in the range405 to 415° C.

According to a preferred embodiment said heating is performed in one ormore heat exchangers. Preferably said heating is at least partlyperformed by recovery of heat from one or more process streams.

In a preferred embodiment, the heating is performed by indirect heatexchange with a heat transfer medium such as supercritical water. By useof such heat transfer medium it is obtained that both the feed mixtureand the product mixture may flow inside tubes thereby allowing foreasier cleaning.

By said heat recovery it is obtained that the process becomes veryenergy efficient as most of the heat required is recovered. In manyembodiments at least 40% of the energy required to heat the feed mixtureto the desired reaction temperature is being recovered such as at least50% of the energy required to heat the feed mixture to the desiredreaction temperature is being recovered. Preferably, at least 60%required to heat the feed mixture to the desired reaction temperature isrecovered such as at least 70% of the energy required being recovered.

4. Reaction

Subsequent to heating to reaction temperature said pressurized andheated feed mixture is maintained at the desired pressure andtemperature in a reaction zone c. for a predefined time. The feedcharacteristics and/or the combination of pressure and temperaturegenerally allow for shorter reaction times and/or a more reacted liquidhydrocarbon product than in the prior art without sacrificing the yieldand/or quality of the desired product. The predefined time in saidreaction zone may according to an embodiment be in the range 1 to 60minutes such as 2 to 45 minutes, preferably said predefined time in saidreaction zone is in the range 3 to 30 minutes such as in the range 3 to25 minutes, more preferred in the range 4 to 20 minutes such as 5 to 15minutes.

5. Cooling

The outlet stream from the reactor comprising liquid hydrocarbonproduct, water with water soluble organics and dissolved salts, gascomprising carbon dioxide, hydrogen, and methane as well as suspendedparticles from said converted carbonaceous material is subsequentlycooled to a temperature in the range 80° C. to 250° C. such as in therange 100 to 200° C.; preferably the outlet stream from the reactor iscooled to a temperature in the range 120° C. to 180° C. such as to atemperature in the range 130° C. to 170° C. by heat exchange with theincoming feed mixture in the heat exchangers.

A preferred embodiment is where said heat exchange is performed byindirect heat transfer via a heat transfer medium such as supercriticalwater, hot oil or molten salt. By use of such indirect heat transfer viaa heat transfer medium it is obtained that both the feed mixture and theproduct mixture can flow inside tubes thereby allowing for easiercleaning. The heat transfer medium may optionally be further heatedand/or be further cooled so as to allow for added controllability andflexibility of the heating and cooling. Said heat transfer medium mayalso be used for transfer of heat to/from other unit operations of theprocess such as e.g. the pretreatment 1 and/or the upgrading part of aprocess.

6. Pressure Reduction

According to a preferred embodiment, the pressurization system comprisestwo or more pressure de-amplifiers each comprising cylinders with apiston equipped with driving means for receiving a force to the pistonsuch as shown and described in connection with FIG. 2-9 . Advantageousdriving means for the pistons in the cylinders include hydraulicallydriven means.

The cooled product mixture thereafter enters a pressure reducing device,where the pressure reduction unit comprises at least one inlet and anoutlet, the pressure reduction unit being adapted to receive apressurized fluid at process pressure level at the inlet, being adaptedto isolate the received pressurized fluid from the upstream process andfrom the outlet and being adapted to reduce the pressure of the fluid toa lower predetermined level and further being adapted to output thefluid through the outlet while still isolated towards the upstreamprocess.

In general pressure reduction unit comprises an actuated valve at theinlet and an actuated valve at the outlet and between the inlet valveand the outlet valve a pressurization device. Further a pressurereduction unit according to an embodiment comprises means for measuringthe pressure upstream the inlet valve, between the inlet valve and theoutlet valve and downstream the outlet valve.

The pressure reduction unit may further comprise a pump unit having acylinder and a piston as well as means for driving the piston inside thecylinder. Advantageously the pressure reduction unit further comprises aposition indicator indicating the cycle position of the pressurereduction device and being adapted to provide a control signal foropening or closing at least one valve in the pressure reduction system.

In one embodiment the pressure reduction unit further comprises acontrol system, where the control system is adapted to allow opening ofthe valves when a certain maximum pressure difference is present oneither side of the valve to be opened.

Often the pressure reduction system is operated so that the inlet valveafter having allowed inflow of a feed stream is closed for a periodbefore the outlet valve is opened, hereby allowing the pressure to bereduced in pressure reduction device.

In order to minimize the pressure loss over the inlet valve and therebythe wear, the outlet valve may be closed for a period before the inletvalve is opened, hereby allowing pressure to be generated in thepressure reduction device in a predefined way. The overlap of closedinlet and outlet valves corresponds to between 5 and 30% of the workingcycle, preferably between 10 and 20% of the working cycle.

A pressure reduction arrangement, typically comprises two or morepressure reduction units being arranged in parallel and/or in series.The working cycles of the individual pressure reduction units of thepressure reduction arrangement be evenly distributed corresponding tothe number of pressure reduction units.

Further the pressure reduction arrangement may include a positionindicator each pressure reduction device, indicating the cycle positionin the device and being adapted to provide a control signal forcontrolling the distribution of the pressure reduction unit cycles.

In general, the pressure in the high pressure processing system isreduced comprising entering a volume of pressurized fluid into apressure reduction device closing the entry of pressurized fluid andexpanding the entered volume to a desired pressure level by increasingthe pressure reduction device volume, removing the fluid at the desiredpressure level from the pressure reduction device by reducing thepressure reduction device volume.

The speed of the pump is in many applications in the in the range 5-50cycles per minute, preferably 5-25, most preferred 5-15 cycles perminute.

An advantageous embodiment of a pressure reduction device where thepressure reduction pump is connected to a further pump that drives apressurization of the energy absorption reservoir. For example thepressure reduction device further comprising an energy reservoir, wherethe pump is operatively connected to the reservoir and where the energyabsorbed by the pump is converted and transferred to the reservoir forsuccessive utilization. In a preferred embodiment a pressurization pumpis provided for supplying additional pressure to the input side of thepressurization equipment in order to compensate for loss of pressureenergy in the system.

In a preferred embodiment, the energy reservoir drives a pressurizationpump adapted to pressurize the feed mixture in the pressurization step(step 2 above) of the high pressure process. In one embodiment, this isperformed by a low pressure turbine connected to a generator generatingelectrical energy, and the electricity generated reduces the energyrequired to drive the pressurization pump in the pressurization step.

The surface area of the pistons is typically dimensioned so as toamplify the pressure i.e. the surface area of each end of the piston isdimensioned so as to obtain a predefined pressure ratio on each side ofthe piston. The ratio of surface area on the low pressure side of thepiston to the surface area on the high pressure side of the piston mayaccording to an embodiment be in the range 1 to 20 such as in the range1 to 10. Preferably the ratio of surface area on the low pressure sideof the piston to the surface area on the high pressure side of thepiston is in the range 1 to 3 such as in the range 1 to 2.

The pressure reducing device are typically designed for low strokespeeds (large stroke volume) thereby allowing for the use of actuatedvalves for filling and emptying of the cylinders rather than checkvalves. Preferred actuated valves include gate valves and ball valves ora combination thereof.

The stroke speed of the pistons according to an embodiment may be fromabout 1 stroke per minute up to about 150 strokes per minute such asfrom about 5 strokes per minute up to about 100 strokes per minute.Preferably the stroke speed of the pistons are from about 10 to about 80strokes per minute such as a stroke speed of the piston in the range 20strokes per minute to about 60 strokes per minute. Besides allowing forthe use of actuated valves the low stroke speed of the piston reducesthe wear on pistons, seals and valve seats.

Often the pressure amplifiers are further designed as double actingpistons as shown in FIG. 1 .

The pressure reducing unit are further designed so as to maximize thecleaning effect of the piston by minimization of the dead space in thecylinder.

Still further the pressure amplifiers may be equipped with positionersto monitor and control the position of the piston at any given moment.The piston positioners are preferably incorporated into the cylinderrod. The positioners are used to control the position of the piston. Thepositioners of the pressure cylinders may also be used to extract a flowmeasurement of media being pressurized by the both individual cylinderand the pressurization system i.e. the volumetric flow rate of theindividual cylinder is given by the stroke volume multiplied by thenumber of strokes over a given time interval, and the same totalvolumetric flow rate may be extracted as the sum of the volumetric flowmeasurements of the individual cylinders.

The positioner(-s) may further be used for synchronization of thestrokes of the individual pressure amplifiers e.g. when the feed in acylinder is being pressurized, another cylinder(s) is being charged withfeed mixture. After the cylinder has been charged, the cylinder ispre-pressurized to a pre-defined level by initiating the stroke with thevalve towards the process closed. When the first cylinder has reached acertain stroke length, the actuated valve towards the process is closedand the equivalent valve towards the process for the next cylinder withpre-charged and pre-pressurized feed mixture to be pressurized isopened. By applying such sequence the pressure drop over the actuatedvalve towards the process and consequentially valve wear and pressurefluctuations are minimized.

The pressure fluctuations may be further reduced by the use of at least2 and preferably 3 or more pressure reducing units in a parallelarrangement according to a preferred embodiment. The control of theindividual pressure reducing units may be adapted so they are operatedin a sequential manner to damp and minimize pressure fluctuation whenswitching from one pressure amplifier to the next.

For many embodiments, where 3 or more cylinders are present these areequipped with sealing means such as double valves so that an individualcylinder can be sealed off and safely exchange an individual cylinder,while other cylinders are kept operating. A more robust, easy tomaintain pressurization arrangement having a high availability is herebyobtained.

Reverse pump cylinder 1 is filled through V1 until cylinder has reacheda given stroke that allows media to decompress by moving cylinder pistonfurther towards end of stroke. Before moving piston to end of stroke, V1closes.

After decompression V2 opens and the hydraulic cylinder presses thedecompressed fluid out of the cylinder to phase separation. Cylinder 1does not empty completely as it is necessary to withhold enough fluid topressurize to process pressure by compression with V2 closed.

The reason is to avoid pressure drop across V1 when it is time to reopenfor next filling.

Simultaneously when V1 closes, V3 opens. Before V3 can open theremaining fluid from the latter stroke is pressurized to preventexcessive wear of valve seats.

The inlet temperature to the pressure amplifying cylinders is generallyin the range from about 10° C. to about 250° C. such as from about 20°C. to about 220° C.; preferably the inlet temperature to the pressureamplifying cylinders is in the range from about 50° C. to about 210° C.such as from about 80° C. to about 200° C.; even more preferably theinlet temperature to the pressure amplifying cylinders is in the rangefrom about 100° C. to about 180° C. such as from about 120° C. to about170° C.

For applications, where the temperature exceeds about 120° C. such asabout 140° C., the cylinders may further be equipped with means forcooling the seals of piston in order to withstand the operatingconditions as shown and described in connection with FIG. 9 above.

7. Separation

The depressurized mixture from said pressure reduction containing liquidhydrocarbon product is subsequently lead to separation. The separationmay comprise means for separating gas from said mixture. Said separationmeans may comprise a flash separator or degasser, wherein gas iswithdrawn from the top. Said gas may be used to produce heat for heatingin the process to the process as shown in the figure and furtherdescribed above. The gas may optionally be cooled to condense compoundssuch as e.g. water prior to said use to produce heat for heating in theprocess.

A particularly preferred embodiment includes a system where theconverted feed mixture/product mixture is first cooled to a temperatureof 60 to 250° C., expanded to a pressure in the range from about 15 toabout 150 bars such as in the range from about 50 to about 120 bars andled to a phase separator/degasser for separation of the product mixtureinto at least a gas phase and residual phase. Preferably the separatedgas phase is first cooled to a temperature in the range 80 to about 200°C., expanded to a pressure in the range 60 to 110 bars such as in therange 70 to 100 bars and led to a phase separator/degasser forseparation of the converted feed mixture/product mixture into at least agas phase and a residual phase.

As further exemplified below, the gas phase often comprises carbondioxide, hydrogen, carbon monoxide, methane, ethane, ethane, propane,iso-propane, butane, iso-butane, water, methanol, ethanol, acetone.

An advantageous embodiment includes extracting/separating hydrogen fromthe separated gas phase and introducing it into said process forupgrading of the hydrocarbons (optional step 8)

An embodiment comprises extracting/separating hydrogen from theseparated gas phase by a membrane gas separation technique. Anotherembodiment comprises extracting/separating hydrogen using a pressureswing adsorption technique. A further embodiment comprisesextracting/separating hydrogen from said separated gas phase by thesteps of:

-   -   separating the converted feed mixture/product mixture into a gas        phase and a residual phase    -   cooling the separated gas to a temperature in the range from        about 31 to 50° C. and separating the cooled gas phase into a        condensed phase substantially free of hydrogen and a residual        gas phase enriched in hydrogen and carbon dioxide in a phase        separator,    -   further cooling the separated gas phase to a temperature in the        range from about 10 up to about 31° C. and separating the cooled        residual gas phase into a liquid phase comprising CO₂ and a        residual gas phase enriched in hydrogen in a separator.    -   introducing the hydrogen enriched gas in the upgrading process        after the pressurization step.

The separating means may further provide at least a coarse separation ofthe degassed mixture into a liquid hydrocarbon rich stream and residualwater rich stream e.g. by gravimetric separation in a 3-phase separator.

The water rich stream comprising water soluble organics, suspendedparticles and dissolved salts may be at least partly withdrawn from saidgravimetric separator, and fed to a recovery unit, optionally afterfurther separation by gravimetric means filtering and/or centrifugationto remove suspended particles.

The degassed mixture or optionally the liquid hydrocarbon rich stream,is withdrawn from said gas separating means, and may be furtherseparated e.g. the liquid hydrocarbon rich stream may be required to beefficiently dehydrated and/or desalted/deashed before being introducedinto the upgrading part of the process.

In many aspects said further separation comprises one or moregravimetric separation step(-s) optionally equipped with means forcoalescing oil or water droplets such as one or more electrostaticcoalescing steps. In other aspects said further separation may includeseparation in one or more centrifugation step(-s) such as separation inone or more 3-phase centrifuges such as one or more high speed disc bowlcentrifuges and/or one or more decanter centrifuges.

Often the operating temperature of the further separation is selected soas to obtain a dynamic viscosity of the liquid hydrocarbon product inthe range from about 1 to about 30 centipoise during said furtherseparation such as in the range from about 1 to about 25 centipoiseduring said further separation, preferably the temperature of theseparation is selected so as to obtain a dynamic viscosity in the rangefrom about 1 to about 20 centipoise such as in the range 5 to 15centipoise.

The operating temperature of said further separation may according to anembodiment be in the range 80 to 250° C. such as in the range 120 to200° C., preferably at least the first of said further separation isoperating at a temperature in the range 130 to 180° C. such as atemperature in the range 150-170° C.

The operating pressure of said further separation may according to anaspect be in the range 10 to 120 bar, such as in the range 15-80 bars,preferably said further separation is operating at a pressure in therange 25 to 50 bar, such as in the range 30-50 bars.

Many aspects relates to the use of one or more phase separators, wherethe residence time in each of the phase separators is in the range 1-30minutes such as in the range 1 to 20 minutes, preferably the residencetime in each of the separators are in the range 2 to 15 minutes.

In a further aspect a viscosity reducing agent may be added to theconverted feed mixture before and/or during the further separation. Theviscosity reducing agent may often be an organic solvent having aboiling point below 200° C. such as below 150° C., preferably below 140°C. such as below 130° C.

The weight ratio of the viscosity reducing agent added to the amount ofrenewable oil may according to many embodiments be in the range 0.01 to2 such as in the range 0.05 to 1, preferably the weight ratio of theviscosity reducing agent added to the amount of low sulphur oxygencontaining renewable oil is in the range 0.1 to 0.5 such as in the range0.1 to 0.4. More preferably the weight ratio of the viscosity reducingagent added to the amount of low sulphur oxygen containing renewable oilis in the range 0.2 to 0.4 such as in the range 0.2 to 0.35.

A particularly preferred embodiment is where the viscosity reducingagent comprises at least one ketone such as Methyl Ethyl Ketone (MEK)and/or 2-heptanone and/or 2,5 dimethyl-cyclo-pentanone or a combinationthereof.

Advantageously the viscosity reducing agent comprises a fraction of thelow oil and is recovered down stream of said further separation step andprior to providing the low sulphur oxygen containing renewable oil tosaid optional upgrading step.

The viscosity reducing agent is recovered in an evaporation stepoperating at a temperature in the range 100-200° C. such as in the range100-160° C., preferably the viscosity reducing agent is recovered in anevaporation step operating at a temperature in the range 100-150° C.such as in the range 100-130° C.

The viscosity reducing agent is substantially recovered in one or moreflash distillation step(-s) producing a low sulphur containing oil phaseand a distillate phase, and where the flash temperature is in the range100-200° C. such as in the range 100-160° C., preferably the viscosityreducing agent is recovered in the flash distillation step producing alow sulphur containing oil phase and a distillate phase, where the flashtemperature is in the range 100-150° C. such as in the range 100-130° C.

A washing agent comprising water may according to another aspect beadded to the liquid hydrocarbon product before or during said furtherphase separation step in order to further control the salt/ash contentof the oil before being introduced to the upgrading step. The washingagent comprising water may be introduced in several steps.

The weight ratio of the washing agent comprising water to oil mayadvantageously be in the range 0.05 to 5.0 such as a weight ratio of thewashing agent comprising water to the oil is in the range 0.05 to 3.0,preferably the of the washing agent comprising water to the oil is inthe range 0.1 to 2.0 such as a weight ratio in the range 0.1-1.0.

The washing agent comprising water may according to an embodimentfurther comprise an acidification agent such as acetic acid or citricacid. The acidification agent may be added so as to obtain a pH of thewater phase after separation of the washing agent comprising water inthe range 2 to 7 such as a pH in the range 2.5 to 6.5, preferably theacidification agent is added so as to obtain a pH of the water phaseafter separation of the washing agent comprising water in the range 2.75to 6 such as a pH in the range 3 to 5.5.

The further separation may according to an embodiment further compriseone or more filtration step(-s) of the liquid hydrocarbon product. Thefiltration step may according to some preferred aspects comprise thefirst step of the further separation and/or the filtration step may be afinal step before optionally introducing the oil to an upgradingprocess.

8. Recovery

The water phases from the gas separating means, and further separationmeans are fed to a recovery device, where liquid organic compounds inthe form of water soluble organics and/or homogeneous catalysts arerecovered in a concentrated form, and recycled to into the feed mixturepreparation device 1. As mentioned above under 1. Preparation the watersoluble organics present in said water phase comprise a complex mixtureof hundreds of different compounds including one or more compounds ofketones, alcohols and poly alcohols, phenols and alkylated phenols,carboxylic acids, furans, alkanes, alkenes, toluene, cumene etc.

Preferably said recovery device, comprises one or more evaporationstep(-s), wherein water is evaporated from said combined water phases,and thereby providing a distillate and a concentrate. The degree ofconcentrating is selected so as to provide a distillate amount thatcorresponds to the amount of water added with the carbonaceous material,homogeneous catalyst and make up base in the pretreatment. Typically theratio of concentrate to the combined water phases entering the recoveryunit is typically in the range from about 0.1 to about 0.9 such as inthe range 0.2 to 0.8. Often the ratio of concentrate to the combinedwater phases entering the recovery unit is in the range from about 0.25to about 0.7 such as in the range 0.3 to 0.6. In other embodiments theratio of concentrate to the combined water phases entering the recoveryunit is typically in the range from about 0.25 to about 0.6 such as inthe range 0.3 to 0.6.

The combined water phases may be preheated to a temperature of e.g.70-130° C. such as a temperature in the range 80 to 115° C. beforeentering into said evaporator. The heat for said preheating ispreferably provided by heat recovery from a process stream and/or fromthe outgoing distillate stream before entering into the evaporator. Inthe evaporator, water is evaporated from said mixture comprising watersoluble organics and dissolved salts at a temperature from about 100 toabout 115° C. In these cases the heat recovery from said process streammay be performed via a heat transfer medium such as a hot oil.

The pH of the combined water phase entering the recovery is preferablymaintained at alkaline conditions such as in the range 7 to 14 such as apH in the range 8 to 12, preferably the pH of the water phase to therecovery unit is maintained in the range 8 to 11. Operating at suchinlet pH to the recovery unit has the advantage of reducing the amountof phenolics in the distillate.

An embodiment of said recovery step is where the recovery step comprisesone or more flash step(-s).

A preferred embodiment of said recovery step is where the recovery stepcomprises evaporation in two or more steps operating at a decreasingpressure and temperature and each being heated with the evaporated vaporfrom the foregoing step to minimize the heat required for theevaporation.

The evaporator may advantageously further comprise condensing saidevaporated vapor in two or more condensation steps, where thecondensation temperatures in said condensation steps are decreasing soas to obtain a fractionation of the evaporated fraction i.e. a fractioncomprising water and eventually higher boiling compounds, and a fractionwhere compounds having a boiling point temperature lower than water areconcentrated.

Preferably said evaporated vapor passes a demister and/or a foam breakerprior to condensation of said evaporated fraction by cooling.Advantageously the evaporator may further be equipped with a coalesceran absorber, where the evaporated fraction is contacted with anabsorbent. Said absorbent comprises in a particularly preferredembodiment a base such as sodium hydroxide.

The evaporator may in some embodiments include increasing thecondensation temperature of said evaporated water by increasing thepressure by a blower, compressor (Mechanical Vapor Recompression) or asteam jet ejector (Thermal Vapor Recompression) or a combinationthereof.

Thereby the evaporated water vapor can be used as a heating medium forthe evaporation in said evaporator, and said evaporator becomes veryenergy efficient as the latent heat of evaporation does not need to besupplied to said evaporation step.

It should be noted that said condensers may comprise heat exchangerswhere the media to be concentrated are evaporated on the other side, butin general said evaporation step comprises at least one additionalcondenser compared to the number of evaporation steps.

The fraction comprising evaporated water (“distillate”) may further becooled to a temperature suitable for discharge in a cooler. Hereby, itis obtained that said evaporator besides recovering said liquid organiccompounds and/or homogenous catalysts also cleans and purifies the waterphase in an efficient manner, and can produce a water phase that may bereused or discharged to a recipient. Optionally the “distillate” may besubjected to one or more polishing steps. Said polishing steps mayinclude a distillation and/or stripping and/or an absorber and/oradsorber and/or a coalescing step and/or a membrane system such asreverse osmosis and/or a biological treatment system such as abioreactor.

The fraction being concentrated with compounds having a boiling pointlower than water may according to a preferred embodiment be mixed withthe concentrate from said evaporator, and recycled to the feed mixturepreparation step 1.

In many applications a bleed or purge stream is withdrawn from saidconcentrated water phase prior to recycling to the feed mixturepreparation step 1 to prevent build up of compounds such as chloride.The bleed stream may according to an embodiment comprise up to about 40%by weight of the concentrated water phase from the recovery unit such asup to about 25% by weight of the concentrated water phase from therecovery unit. Preferably the bleed stream comprises up to about 20% byweight of the concentrated water phase from the recovery unit such as upto about 15% by weight of the concentrated water phase from the recoveryunit. More preferably the bleed stream comprises up to about 10% byweight of the concentrated water phase from the recovery unit such as upto about 5% by weight of the concentrated water phase from the recoveryunit. The bleed stream may be disposed off. However, in manyapplications the bleed stream is further treated.

The concentrated water phase from the recovery unit typically has apositive heating value.

A preferred application comprises further treating the bleed stream bycombustion and/or co-combustion in a boiler or incinerator. Optionallythe bleed stream is further concentrated prior to said combustion and/orco-combustion.

A particularly preferred embodiment comprises further treating the bleedstream in an ion exchange step. The concentrated water phase from therecovery unit may be filtered to remove eventual solids prior toentering said ion exchange step.

The ion exchange step may comprise one or more ion exchange steps suchas one or more ion exchange resin(-s) contained in one or more fixedbeds.

Said one or more ion exchange steps may be arranged with one or morefixed bed(-s) in parallel and/or one or more fixed bed(-s) in series.

An advantageous embodiment comprises further treating the bleed streamcomprises at least two fixed bed(-s), each containing a chlorideselective ion exchange resin capable of selectively adsorbing chloridefrom said concentrated water phase from said recovery unit and arrangedvalves in a parallel arrangement so that at least one ion exchange bedis online and at least one ion exchange bed is offline. Herebycontinuous operation is ensured and chloride removal can be continued inthe ion exchange bed(-s) being online while ion exchange bed(-s) beingoffline can be cleaned. Said cleaning may according to an embodiment beperformed by a back flow or back flushing of the ion exchange bed(-s) bydemineralized water such as distillate water from the recovery unit. Avalve arrangement and/or control system is included allowing for suchcleaning or regeneration by back flow or back flush with demineralizedwater.

Typically the chloride removal in said ion exchange step is at least 50%of the chlorides in the concentrated water phase entering said ionexchange step such as a chloride removal of at least 60%. In manyembodiments the chloride removal in said ion exchange step is at least70% of the chlorides in the concentrated water phase entering said ionexchange step such as at least 80%. The chloride depleted stream fromsaid chloride ion exchange step is preferably recycled to the feedmixture preparation step 1.

Further, in many embodiments the amount of homogeneous catalyst(-s) inthe form of potassium and/or sodium such as being retained in saidchloride depleted outlet stream from said chloride ion exchange step isat least 70% by weight of the amount entering said chloride ion exchangestep such as at least 80% by weight. Preferably, the amount ofhomogeneous catalyst(-s) in the form of potassium and/or sodium such asbeing retained in said chloride depleted outlet stream from saidchloride ion exchange step is at least 85% by weight of the amountentering said chloride ion exchange step such as at least 90% by weight.Hereby, less make up homogeneous catalyst is required to be added in thepretreatment step 1, and a more economical process is obtained forproviding crude oil to the upgrading process, and thereby an overallmore efficient and economical process is obtained.

9. Upgrading (Optional)

The crude oil produced in step 1 may be optionally be further subjectedto an upgrading step to finished transportation fuels, lubricants and/orfinished fuels.

The invention claimed is:
 1. Pressurization unit for use in processingequipment handling high pressure fluid, where the pressurization unitcomprises at least one inlet and an outlet, the pressurization unitbeing adapted to receive a feed fluid at a feed pressure level at theinlet, being adapted to isolate the received feed fluid from the inletand from the outlet and being adapted to increase the pressure of thefeed fluid to a higher predetermined level and further being adapted tooutput the fluid through the outlet into the high pressure process whilestill isolated towards the inlet, the unit comprising an actuated valveat the inlet and an actuated valve at the outlet and further apressurization device between the inlet valve and the outlet valve,wherein the pressurization device includes a pump including first,second, and third cylinders, and first, second, and third pistonsattached to a common piston rod and driven inside the first, second, andthird cylinders, respectively, wherein the inlet valve and the outletvalve are fluidly connected to a first cylinder volume inside the firstcylinder defined by a position of the first piston, wherein an energystorage is fluidly connected via a control valve to a second cylindervolume inside the second cylinder defined by a position of the secondpiston, wherein a supply of pressure control fluid is fluidly connectedvia another control valve to a third cylinder volume inside the thirdcylinder defined by a position of the third piston, wherein the pump isconfigured to transfer energy from a flow of energy recovery fluid fromthe energy storage through the second cylinder volume to the flow of thefeed fluid through the first cylinder volume, and transfer energy fromthe flow of the pressure control fluid through the third cylinder volumeto the flow of the feed fluid through the first cylinder volume, inorder to increase the pressure of the feed fluid to the higherpredetermined level, and within a pump cycle of the pressurizationdevice during which each of the inlet valve and the outlet valvealternates between open and closed states, the inlet valve after havingallowed inlet of a feed stream is closed for a period before the outletvalve is opened, hereby allowing pressure to be generated by thepressurization device and the outlet valve is closed for a period beforethe inlet valve is opened, hereby allowing pressure to be reduced in thepressurization device, such that the inlet valve is opened a differentamount of time than the outlet valve during the pump cycle, wherein theopen and closed states of both the inlet and outlet valves arecontrolled by control signals issued by a controller, and a positionindicator is provided indicating the cycle position of thepressurization device and being adapted to provide a control signal foropening and closing of each of the inlet and outlet valves in thepressurization unit, the pressurization unit further comprising acontrol system, where the control system is adapted to allow opening ofthe valves when a certain maximum pressure difference is present betweeneither side of the valve to be opened.
 2. Pressurization unit accordingto claim 1, wherein a pressure transducer is provided for measuring thepressure upstream the inlet valve, between the inlet valve and theoutlet valve and downstream the outlet valve.
 3. Pressurization unitaccording to claim 1, wherein the overlap of closed inlet and outletvalves correspond to between 5 and 30% of the working cycle. 4.Pressurization unit according to claim 1, wherein channels or conduitsfor cooling fluid are provided in the piston and being adapted to keepthe temperature of the piston at a predetermined level relative to thesealing region of the piston.
 5. Pressurization arrangement comprisingtwo or more pressurization units according to claim 1, thepressurization units being arranged in parallel and/or in series. 6.Pressurization arrangement according to claim 5, wherein the workingcycles of respective pressurization devices within the two or morepressurization units are evenly distributed corresponding to the numberof pressurization units.
 7. Pressurization arrangement according toclaim 1, wherein a position indicator is provided for the pressurizationdevice, indicating the cycle position of the device and being adapted toprovide a control signal for controlling the distribution of thepressurization device cycles.
 8. A method for pressurizing a highpressure processing system, the method comprising entering a volume ofpressurized fluid into a pressurization device of a pressurization unitaccording to claim 1, closing the entry of pressurized fluid andpressurizing the entered volume of fluid to a desired pressure level bydecreasing the pressurization device volume, removing the volume offluid at the desired pressure level from the pump by further reducingthe pump volume.
 9. A method according to claim 8, wherein the speed ofthe pressurization device is in the range 5-50 cycles per minute.
 10. Amethod according to claim 1, wherein a control signal generated as anoutput from a pressure reduction system measurement is used to controlthe pressurization unit or pressurization arrangement.
 11. A highpressure process system comprising a pressurization unit or apressurization arrangement of two or more pressurization units accordingto claim
 1. 12. Pressurization arrangement comprising two or morepressurization units according to claim 2, the pressurization unitsbeing arranged in parallel and/or in series.
 13. Pressurizationarrangement comprising two or more pressurization units according toclaim 3, the pressurization units being arranged in parallel and/or inseries.
 14. Pressurization arrangement comprising two or morepressurization units according to claim 4, the pressurization unitsbeing arranged in parallel and/or in series.
 15. Pressurizationarrangement according to claim 2, wherein a position indicator isprovided for a pressurization device, indicating the cycle position ofthe device and being adapted to provide a control signal for controllingthe distribution of the pressurization device cycles.
 16. Pressurizationarrangement according to claim 3, wherein a position indicator isprovided for a pressurization device, indicating the cycle position ofthe device and being adapted to provide a control signal for controllingthe distribution of the pressurization device cycles.
 17. Pressurizationunit according to claim 1, wherein the pressurization unit isselectively controlled by the controller to operate in a pressurizationmode in which the pump transfers energy from the flow of the energyrecovery fluid and the pressure control fluid through the second andthird cylinder volumes, respectively, to the flow of the feed fluidthrough the first cylinder volume in order to increase the pressure ofthe feed fluid to the higher predetermined level, and a pressurereduction mode in which the pump transfers energy from the flow of thefeed fluid through the first cylinder volume to the flow of the energyrecovery fluid through the second cylinder volume in order to reduce thepressure of the feed fluid, wherein the energy storage is configured tostore pressure resulting from the transfer of energy from the flow ofthe feed fluid through the first cylinder volume to the flow of theenergy recovery fluid through the second cylinder volume while thepressurization unit operates in the pressure reduction mode, the storagebeing configured to supplement the transfer of energy to the flow of thefeed fluid through the first cylinder volume while the pressurizationunit operates in the pressurization mode.
 18. Pressurization unitaccording to claim 17, wherein during each pump cycle of thepressurization device, the respective amounts of time in which the inletvalve and the outlet valve are open vary according to whether thepressurization unit is operating in the pressurization mode or thepressure reduction device, such that the inlet valve is open a smalleramount of time than the outlet valve during each pump cycle in which thepressurization unit is operating in the pressurization mode, and theinlet valve is open a larger amount of time than the outlet valve duringeach pump cycle in which the pressurization unit is operating in thepressure reduction mode.